The release is available now in two versions: Full and Active. The Full Release includes all source vocabularies. The Active Release includes only vocabularies that are actively updated in the Metathesaurus. The Active Release is a smaller download, decreases MetamorphoSyS processing time, and provides easier access to current Metathesaurus content.

Data Changes

Some fields in the RRF files have changed their allowable character length, which could affect those loading the Metathesaurus into a database. See the full list of changes for details.

2013AA is the last release that will include the co-occurrences files: MRCOC.RRF and MRCOC (ORF format). Co-occurrence information will remain on the NLM Web site; more details will be provided with the 2013AB release in November.

Logical Observation Identifier Names and Codes (LOINC)

The representation of LOINC (SAB=LNC) in the Metathesaurus does not include the following content: